A lift going up at half g.

Water rises 3 cm in a capillary tube at rest. The same tube and beaker are placed in a lift accelerating upward at g/2. The water now rises to:

Answer: 2 cm.

In a lift accelerating upward at a, the effective gravity is g + a, so the raised column feels heavier. The capillary rise is inversely proportional to the effective gravity.

h' = h \frac{g}{g + a} = 3 \times \frac{g}{1.5 g} = 2 cm

The water rises only 2 cm. Accelerating upward makes the column heavier, so surface tension can hold up less of it; accelerating downward, or falling freely, does the opposite.

Original practice question · JEE Physics Decoded

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A lift going up at half g.

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